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2003 Mustang GT - Rear Tire Size Question

  • Thread starter Thread starter Cassiebaebae
  • Start date Start date Jun 29, 2026
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Cassiebaebae

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#1
  • Jun 29, 2026
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Hii Everyone Im new here! Looking for someone to help with my rear tires the rims are cobra 17x10.5’s im looking for something to fill up the rear wheel well my friend told me to get these tires (275/40r17) and they look hideous on my car thank you in advance.
 
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Bronco2fan

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Jun 29, 2026
#2
  • Jun 29, 2026
  • #2
315's
 
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Cassiebaebae

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#3
  • Jun 30, 2026
  • #3
Bronco2fan said:
315's
Click to expand...
Tyy sm… Is there any numbers besides that? I want it to fill up the wheel wells it looks dumb
 

gkomo

now i can hopefully expect to receive the shaft
Aug 2, 2024
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Jun 30, 2026
#4
  • Jun 30, 2026
  • #4
Fill up the wheel well in what way? width or height? as mentioned 315's will satisfy the width requirement, but if the car isn't lowered there will always be a gap between the tire and fender. Is the car lowered at all?
 
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Cassiebaebae

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  • Jun 30, 2026
  • #5
gkomo said:
Fill up the wheel well in what way? width or height? as mentioned 315's will satisfy the width requirement, but if the car isn't lowered there will always be a gap between the tire and fender. Is the car lowered at all?
Click to expand...
No the tires on it now look small they are 275/40r17s what would make them taller sorry for dumb questions lol new to all this ty! So 315 what? i know the rims are 17’s
 

squeak93

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315/35 17 should be what you are looking for. 25.7 height which is right at factory and same as those 275/40.

HOWEVER - if you want a taller tire to actually fill out a non lowered wheel well you'll have to measure etc and find the appropriate sidewall height etc. Usually lowering a car is the best solution etc.

What is front tire size and are you trying to match that height? (FWIW, a 275 on that 10.5 wheel probably looks super stretched).
 
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Cassiebaebae

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  • Jun 30, 2026
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squeak93 said:
315/35 17 should be what you are looking for. 25.7 height which is right at factory and same as those 275/40.

HOWEVER - if you want a taller tire to actually fill out a non lowered wheel well you'll have to measure etc and find the appropriate sidewall height etc. Usually lowering a car is the best solution etc.

What is front tire size and are you trying to match that height? (FWIW, a 275 on that 10.5 wheel probably looks super stretched).
Click to expand...
I will look and let ya know. Yessss the back tires look crazy! Can you point me in what i need to buy to lower i will post pictures of it when I get home. Ty!
 

Noobz347

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#8
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Don't change your tire height.

The speedo will be off and you would be sacrificing torque for a top end you will never use.
squeak93 said:
315/35 17 should be what you are looking for.
Click to expand...
Do this ^^
 

squeak93

15 Year Member
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#9
  • Jun 30, 2026
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Cassiebaebae said:
I will look and let ya know. Yessss the back tires look crazy! Can you point me in what i need to buy to lower i will post pictures of it when I get home. Ty!
Click to expand...
Lowering springs vs coil overs. HUGE debate there. Lowering springs are cheap and the avg joe can install fairly easily with a jack and some basic hand tools. Coil overs go a bit further with needing specific shocks/struts and similar hand tools etc.

I am an Eibach Sportline fan - I like the car low. That being said my rear springs are now eibach drag launch, but car is still slammed with steeda weight jacker Lower control arms. Fronts are still Sportline but will get replaced with winter with coil overs to complete the drag suspension setup. I might even go rear coil overs this winter as well and go with a straight non coil perch LCA so I can get my freaking sway bar alignment back to somewhat normal. Who knows on how deep my check book goes this winter with everything else.

You can litterally take your pick of specific or progressive rate springs in .5-2.5 drop ranges.

Show pics of the car and list your goals. Street cruiser or drag or road race or somewhere in between?
 
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Cassiebaebae

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Jun 30, 2026
#10
  • Jun 30, 2026
  • #10
Noobz347 said:
Don't change your tire height.

The speedo will be off and you would be sacrificing torque for a top end you will never use.

Do this ^^
Click to expand...
Ok, Idk what the factory tire size is someone painted over the sticker that shows all that info
 

Noobz347

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#11
  • Jun 30, 2026
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Factory Sizes:

Wheel: 17" x 8" aluminum wheel
Tire: 245/45ZR17
 
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Cassiebaebae

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#12
  • Jun 30, 2026
  • #12
squeak93 said:
Lowering springs vs coil overs. HUGE debate there. Lowering springs are cheap and the avg joe can install fairly easily with a jack and some basic hand tools. Coil overs go a bit further with needing specific shocks/struts and similar hand tools etc.

I am an Eibach Sportline fan - I like the car low. That being said my rear springs are now eibach drag launch, but car is still slammed with steeda weight jacker Lower control arms. Fronts are still Sportline but will get replaced with winter with coil overs to complete the drag suspension setup. I might even go rear coil overs this winter as well and go with a straight non coil perch LCA so I can get my freaking sway bar alignment back to somewhat normal. Who knows on how deep my check book goes this winter with everything else.

You can litterally take your pick of specific or progressive rate springs in .5-2.5 drop ranges.

Show pics of the car and list your goals. Street cruiser or drag or road race or somewhere in between?
Click to expand...
The front tires are 245/45zR17. Here is a picture of it from the side can you see the gaps it looks crazy
 

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Cassiebaebae

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#13
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Noobz347 said:
Factory Sizes:

Wheel: 17" x 8" aluminum wheel
Tire: 245/45ZR17
Click to expand...
That would be all the tires right? Cause someone put 17x10.5’s on the back. Sorry im trying to learn about this
 

Noobz347

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Yep... That would be at all 4 corners.

GTs do not come from the factory with staggered wheels.
 
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Cassiebaebae

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#15
  • Jun 30, 2026
  • #15
Noobz347 said:
Yep... That would be at all 4 corners.

GTs do not come from the factory with staggered wheels.
Click to expand...
This is how it looks it just looks crazy to me
 

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gkomo

now i can hopefully expect to receive the shaft
Aug 2, 2024
2,185
1,432
133
San Diego, CA
Jul 1, 2026
#16
  • Jul 1, 2026
  • #16
Ya I think you just need to lower the car
 
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Cassiebaebae

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Jul 1, 2026
#17
  • Jul 1, 2026
  • #17
gkomo said:
Ya I think you just need to lower the car
Click to expand...
Thank you
 

squeak93

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#18
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100% lower it. Springs of your choosing (at least a 1.5 drop IMHO) and some good caster camber plates- Maximum motorsports 4 bolt - buy once cry once.

If you want a tad lower and don't mind a slight creak once in a while, lower without isolators to get another 3/8-1/2 inch.
I wonder if it has drag springs or something on it, that seems like it sits high even for factory - but I've not had a factory height car since 2004 lol.
 
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Cassiebaebae

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Jul 1, 2026
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  • #19
squeak93 said:
100% lower it. Springs of your choosing (at least a 1.5 drop IMHO) and some good caster camber plates- Maximum motorsports 4 bolt - buy once cry once.

If you want a tad lower and don't mind a slight creak once in a while, lower without isolators to get another 3/8-1/2 inch.
I wonder if it has drag springs or something on it, that seems like it sits high even for factory - but I've not had a factory height car since 2004 lol.
Click to expand...
Yessss it looks so weird i def. want it lower. I dont know much about all this but been trying to get my friend to help me figure it out. I seen some 2” springs is that to much?
 

squeak93

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#20
  • Jul 2, 2026
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Depends on how rough your roads are and how much attention you pay. If careful and not trying to off road 2 inch is perfectly fine and will make it look a ton better.

Depending on miles you may look at ball joints and other wear items as lowering will speed up failure on prior worn parts. But don't skip the caster camber plates.
 
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